| 摘要: |
| 建立一种能够模拟实际气候条件下地源热泵竖直U形管换热器长期换热过程的复合数值模型。模型由一个三维模型和一个适配于实际工程问题的二维管群模型配套组成。其中三维模型输出的暂态模拟结果被用作二维模型的输入边界条件。模型能够在耗费相对较小计算量的同时给出较为准确的长期暂态模拟结果。根据杭州当地覆盖一个供冷季、过渡季及一个供暖季的实测数据，整理研究了土壤热力学能关于在实际气温及换热器运行条件下的变化规律、进出口水温波动及其影响因素，并最后分析了长期换热影响下的管群不同深度的温度分布情况。研究发现，在经过一个供冷季，过渡季和供暖季后，半径2 m以内的三维计算区域土壤的热力学能上升了0.292 MJ，与仅受气温影响的情况相比，土壤的相对热力学能增量为1.037 MJ，相对温度增量为0.28 K，反映出长三角用户对冷量的年需求量明显高于对热量的年需求量，多余热量会随时间推移在土壤中产生热堆积，对换热效率起到负面影响。地下1.5 m观测点的温升曲线峰值滞后于地下0.5 m观测点约2周，反映出沿埋管深度较深的点的温升曲线在相位上整体滞后于深度较浅的点。系统运行条件下，整个供冷季和供暖季，地埋管的出水口水温与同时刻气温温差均值分别为-8.313 K和9.077 K。经过对管群的进一步分析，发现热堆积主要集中在7 m以下的土壤层，且在管群的转角处影响半径更大，并随深度增加而缓解。 |
| 关键词: 地源热泵 三维建模 计算速度 地下换热场 |
| DOI： |
| Received:February 08, 2017 |
| 基金项目: |
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| Hybrid 3D and 2D Numerical Models of Geothermal Heat Exchanger for Ground Source Heat Pump System |
|
Zhou Hongyun1, Li Yong1, T. M. Eikevik2, Wang Ruzhu1
|
| (1.School of Mechanical Engineering, Shanghai Jiao Tong University;2.Department of Energy and Process Engineering, Norwegian University of Science and Technology) |
| Abstract: |
| This paper presents the development of a hybrid model for simulating a vertical U-tube geothermal heat exchanger under actual climate. The model consists of a 3D model representing a pair of U-tubes buried in symmetric boreholes and a supplementary 2D model that can be applied to real site scenarios. The temperature series at the wall of the borehole and initial soil temperatures at different depths derived from the simulation results of the 3D model serve as the input boundary conditions of the 2D model. Hence, the hybrid model shares the respective advantages of both subordinate models and therefore provides comprehensive simulation results that span approximately 10 months at a slight cost in implementation complexity. Meanwhile, the model is limited by numerous assumptions such as the consistency between the ground surface and air temperatures and physical uniformity of the materials. Simulations were performed based on the conditions obtained at a real site in the city of Hangzhou. The simulation time range was June 12, 2015, to March 17, 2016, which covered an entire cooling, transition, and heating season. The collected data revealed that the soil within an effective radius of 2 m gained an absolute increase in internal energy of 0.292 MJ after the simulation. The relative increases in the internal energy and average temperature were 1.037 MJ and 0.28 K, respectively, compared to those affected only by climate, which indicated an unwanted accumulation of heat beneath the ground. Moreover, the temperature at a deeper soil depth showed a lag in phase behind that of a shallower depth. This lag was approximately 2 weeks between a point at the center of the entrance and exit of the U-tubes and a point 1 m below it. Moreover, the fluctuation patterns of the inlet/outlet fluid temperatures showed a significant shift from the air temperature toward the annual averages, which were -8.313 K in the cooling season and 9.077 K in the heating season. Finally, the temperature distribution among pipe-clusters at different depths showed that the heat accumulation mainly occurred at a depth greater than 7 m, and the accumulation was more severe at a shallower depth and at the corners of clusters. |
| Key words: ground source heat pump 3 dimensional modelling implementation complexity underground heat transfer field |
